1. Field of the Invention
The present invention relates to a process for producing calcium-supplemented milk drinks, and more specifically, the present invention relates to a process for producing calcium-supplemented milk drinks with good flavor and with no precipitation of calcium salts.
2. Description of the Prior Art
As the principal component of bone and teeth of animals, calcium is an essential element for organisms. It is required that human adults should take a rate of 1.0 g/day while little children should take a rate of 0.6 g/day. In recent years in Japan, the shortage of calcium intake has been remarked, which is a serious problem with relation to osteoporosis.
Nutritionally, cow's milk is essentially a good foodstuff, and if the milk is supplemented with calcium, the calcium shortage can be supplemented by less intake of such milk. The supplementing process in the process of producing calcium-supplemented milk includes the following;
1. a process of adding a soluble calcium salt to cow's milk after heat sterilization, and PA0 2. a process of adding an insoluble calcium salt which is unreactive with milk protein, such as calcium phosphate and calcium carbonate, followed by heat sterilization of the milk.
However, process 1 is disadvantageous in that because the uniquely unattractive flavor of soluble calcium salts such as calcium chloride affects the taste of cow's milk, only a limited amount of these salts can be added to the milk. Furthermore, because ionized calcium reacts with casein and whey protein consequently to decrease the heat resistance of the milk, a sterilization process to prepare a commercially aseptic state is never applicable to the milk. Thus, the milk cannot be prepared as a long-life type. A process is known comprising individually sterilizing milk base and calcium under heat and subsequently mixing them together, but the procedures involved are laborious. Because calcium ions promote the modification of protein into unstable protein and promote also the precipitation thereof even at lower temperatures, furthermore, the amount of calcium ions to be added to the milk is limited so that the milk cannot be supplemented with a satisfactory amount of calcium.
Alternatively, process 2 is problematical in that rough feeling may be caused in the milk unless a particle size of the insoluble calcium salts is very small and in that the calcium salts may readily precipitate because of their insolubility. So as to overcome the problems of the insolubility, various processes have been suggested, for example, a process comprising adding 0.01 to 0.06% by weight of a stabilizer such as carrageenan and gum guar to cow's milk (Japanese Patent Laid-open No. Sho 62-248450): a process comprising depositing insoluble calcium salts in fine particles onto fat spheres in the emulsion of a fat and water or comprising embedding the salts into the fat spheres in the emulsion to adjust the specific gravity of these particles approximately to the specific gravity of the liquid phase (Japanese Patent Laid-open No. Sho 57-110167): a process comprising adding crystalline cellulose to the milk to prepare a fine network structure in the liquid phase, thereby supporting the insoluble calcium salts in fine particles to prevent the precipitation thereof (Japanese Patent Publication No. Sho 57-35945): or a process comprising mixing calcium carbonate in slurry with an aqueous solution of a hydrophilic emulsifier, and subsequently subjecting the mixture solution to a dehydration process, prior to vacuum drying, whereby the aggregation can be prevented (Japanese Patent Laid-open No. Sho 63-173556). However, all of these prior processes have the disadvantage of modifying the properties of cow's milk itself, increasing the calories of cow's milk so that it is not suitable for low-fat milk, or escalating the production cost.
Because it is difficult to prevent the precipitation of calcium salts in general, a process for supplementing cow's milk with calcium is suggested, comprising supplementing milk with fine particles of calcium phosphate or calcium citrate which are recovered from whey as a byproduct of cheese production, characterized in that no precipitation occurs (Japanese Patent Laid-open No. Sho 60-248152). These calcium salts are in a network structure so the salts can keep their stable state with substantially no generation the precipitate from solution. Additionally, the calcium salts are not water-soluble because of their non-ionic state, so that the salts do not react with protein and no precipitation occurs. Because the salts are not crystalline, their network structure can be maintained as is. The salts never crystallize to cause precipitation.
Since the network structure per se of the calcium salts secondarily binds together to be modified into a polymerized state, the salts may therefore precipitate consequently. So as to prevent such precipitation, it is required to preliminarily mix the salts with fat. Due to the consequent calorie increase, the resulting milk is not suitable as low-fat milk, disadvantageously; or the production cost is elevated, disadvantageously.